1. Field of the Invention
The present invention relates to methods, instrumentation, and implants for orthopedic surgery and, more specifically, to rotator cuff sparing procedures and associated devices for shoulder replacement surgery.
2. Discussion of Related Art
Orthopedic surgeons perform joint replacement surgery for patients who suffer pain and physical limitations caused by joint surfaces that have been damaged by degenerative, traumatic, or other pathologic processes. The functional outcome from these joint replacement surgeries is directly related to the degree of morbidity associated with the surgical method and the ability of the method to best restore the natural anatomy and biomechanics of the joint. Orthopedic surgeons are continually searching for ways to improve outcomes for joint replacement surgery by developing methods of less invasive surgery to limit surgical morbidity and by developing novel methods and implants to better restore the native joint anatomy.
Conventional shoulder replacement surgery has several limitations. It requires an extensive exposure that irreversibly damages the rotator cuff and still fails to gain sufficient joint access to properly restore the native anatomic relationships of both the humeral head and glenoid surfaces. Also, there remain issues with glenoid implant fixation and early loosening.
Conventional methods utilize a large anterior deltopectoral exposure. The anterior humeral circumflex blood vessels are typically ligated and the anterior (subscapularis) musculotendinous unit is transected. The shoulder must then completely dislocated both anteriorly and posteriorly to prepare the humeral and glenoid joint surfaces. This can cause excessive traction on the arm which has resulted in injury to the nerves of the brachial plexus (Lynch N M, Cofield R H, Silbert P L, et al. Neurologic complications after total shoulder arthroplasty. J Shoulder Elbow Surg 1996; 5(1):53-61).
With regards to shoulder replacement surgery, all conventional methods require surgical transection of a rotator cuff tendon to gain sufficient exposure of the joint surfaces of the shoulder (See U.S. Pat. No. 4,550,450, entitled, “Total Shoulder Prosthesis System”, the entire contents of which are incorporated herein by reference). After the joint surfaces are replaced, the rotator cuff tendon must be surgically repaired with suture material. This tenuous repair necessitates an obligatory period of approximately six weeks for the rotator cuff tendon to heal before advanced shoulder rehabilitation can be performed. This surgical transection and subsequent repair, as well as the delay in rehabilitation, hold significant consequences for the functional outcome of the shoulder replacement including permanent weakness and decreased range of motion (Miller S L et al., “Loss of subscapularis function after total shoulder replacement: A seldom recognized problem”, J Shoulder Elbow Surg. 2003 January-February; 12(1):29-34).
Additionally, despite the extensive exposure, conventional methods for shoulder replacement surgery still fail to properly restore the native anatomic relationships of the joint surfaces of the shoulder. Conventional methods prepare the humeral surfaces of the shoulder joint by referencing off the intramedullary axis of the humeral shaft. This poses great difficulty for the surgeon since the intramedullary axis has an inconsistent relationship to the humeral surface. The humeral joint surface also possesses a complex anatomy with significant variability which cannot be entirely restored with conventional methods and implants. There exists much variability in the humeral head neck-shaft angle, posterior and medial offset, version (rotation), height, thickness, and radius of curvature. (Boileau P, Walch G, “The Three-Dimensional Geometry of the Proximal humerus”, J Bone Joint Surg Br 1997; 79B: 857-865; Iannotti J P, et al. “The Normal Glenohumeral Relationships. An Anatomic Study of One Hundred and Forty Shoulders”, J Bone Joint Surg 1992; 74A(4):491-500; McPherson E J, et al. “Anthropometric Study of Normal Glenohumeral Relationships”, J Shoulder Elbow Surg 1997; 6:105-112; Soslowsky L J, et al. “Articular geometry of the glenohumeral joint”, Clin Orthop 1992; 285:181-190). The failure to restore the native anatomic relationships and biomechanics to the shoulder joint has proven to result in a significantly lesser functional and durable outcome (Williams G R, et al. “The effect of articular malposition and shoulder arthroplasty on glenohumeral translations, range of motion, and subacromial impingement”, J Shoulder Elbow Surg. 2001; 10(5):399-409).
Conventional methods of shoulder replacement surgery also have difficulty gaining access to the glenoid joint surface. The glenoid surface of the shoulder joint is best prepared by working along an axis perpendicular to its surface. Because the humeral head sits in the way, this is a nearly impossible task with conventional methods. The humeral head has to be partially removed, the subscapularis (anterior shoulder rotator cuff muscle) transected, and the proximal humerus dislocated to even get close to working along this axis. Because of this difficulty, a majority of orthopedic surgeons still choose not to replace the glenoid surface despite clinically proven results of improved pain relief and function for shoulder replacement surgery when both the humeral and glenoid surfaces are replaced. (Boyd A D, Thomas W H, Scott R D, et al. “Total shoulder arthoplasty versus hemiarthroplasty—indications for glenoid resurfacing”, J of Arthroplasty 1990; 5(4):329-336; Gartsman G M, Roddey T S, Hammerman S M. J Bone Joint Surg 2000; 82A(1):26-34; Edwards T B, Kadakia N R, Boulahia A, et al., “A comparison of hemiarthoplasty and total shoulder arthroplasty in the treatment of primary glenohumeral osteoarthritis: Results of a multicenter study”, J Shoulder Elbow Surg 2003; 12(3):207-13; Orfaly R M, Rockwood C A, Esenyel C Z, et al., “A prospective functional outcome study of shoulder arthoplasty for osteoarthritis with an intact rotator cuff”, J Shoulder Elbow Surg 2003; 12(3):214-21.)
Despite improved results of conventional methods when both the humerus and glenoid surfaces are replaced, there still remains limitations with regard to glenoid fixation and early glenoid implant loosening (Boileau P, Avidor C, Krishnan S G, et al., “Cemented polyethylene versus uncemented metal-backed glenoid components in total shoulder arthroplasty: a prospective, double-blind, randomized study”, J Shoulder Elbow Surg 2002; 11(4):351-9). Both, cemented polyethylene and metal backed glenoid components are used in conventional methods. The cemented implant never incorporates with the glenoid bone and with time, the cement-bone interface eventually fails and the implant comes loose. Conversely, the metal-backed glenoid prosthesis has an unacceptable rate of early loosening, at least 20% in one study. However, if the metal-backed implant can remain rigidly fixed to the bone for a sufficient period of time, the bone of the glenoid will eventually adhere to the metal-backed surface and long-term studies have revealed little evidence for late clinical loosening in these cases. Failure of the metal-backed glenoid implant appears to be related to the limitations in achieving sufficiently rigid and durable initial fixation
While performing shoulder replacement surgery for arthritis, associated rotator cuff tears are sometimes discovered and should be repaired when possible. If a less invasive surgical approach is employed to perform the shoulder replacement surgery, a less invasive method of rotator cuff repair that is compatible with the method shoulder replacement surgery must be to be available to simultaneously address these associated rotator cuff tears.